Efficient condensation of vapor and collection of fog from the atmosphere are important to life in arid environments. Nature has come up with various strategies to optimize the processes by a combination of both topographic and chemical functionalization of solid surfaces that are imprinted passively into the structure of the surface. One crucial aspect in this process is the removal of liquid from the solid surface once it has condensed. In here, we present a novel active approach to improve the efficiency of vapor condensation onto hydrophobic surfaces that are functionalized by electrowetting. We fabricated electrowetting-functionalized surfaces with submerged interdigitated electrodes. Upon exposure to supersaturated vapor droplets condense onto these surfaces in an initially random pattern. As the droplets grow, electrowetting mobilizes the growing drops and induces early coalescence, giving rise to alignment of drops and to early shedding. Mobilization and early shedding are controlled by the effective reduction of contact angle hysteresis in AC electrowetting. Drops are found to grow algebraically, initially with a self-similar growth law as in conventional drop condensation. At a later stage, self-similarity is broken and the statistical drop size distribution is altered. We discuss potential applications in terms of heat transfer.

Separation of substances is central to many industrial and medical processes ranging from wastewater treatment and purification to medical diagnostics to artificial lungs. Conventional membrane separation techniques allow particles below a critical size to pass through a membrane pore while inhibiting passage of particles larger than that critical size; membranes that show reversed behavior, i.e., passage of large particle and inhibition of small ones, are unusual in conventional engineering applications. Inspired by endocytosis and the self-healing property of stabilized liquid films [1–3], we demonstrate a membrane-based separation technique where particles smaller than a critical size given the particle inertial properties are retained and larger ones pass through. Distinct from conventional membranes, the dynamically reconfigurable and self-healing nature of liquid membranes allows in-membrane object maneuverability and transport of retained particles. We demonstrate that such membranes can be utilized for a number of applications that are previously unachievable by synthetic membrane technologies.

The microstructures of certain natural surfaces, such as plant leaves, reptile skin and ciliated tissues, can be actuated to provide dynamic, adaptive properties of wetting, transport and adhesion [1]. Here, we dynamically control the wetting properties of a superhydrophobic surface of (hydrophobic) polydimethylsiloxane (PDMS) micropost arrays (2-10 µm post diameter) that can be mechanically deformed to change the post spacing (pitch) and orientation. We show that the static contact angle, contact angle hysteresis, and control of wetting state (from Cassie-Baxter to Wenzel) can systematically controlled by the topographic deformation. The programmed droplet pinning and release for large 10x10 droplet arrays is applied to droplet sorting, selection and mixing. The advantages of this actuation to manipulate surface topographies are scalability, speed of actuation (up to 100 Hz), digital programmability, and surface environments that can be dry or wet. We envision this type of programmable surface area may find applications in diagnostic lab-on-chip with ‘open channel’ microfluidics, as an alternative to more complex electrowetting droplet manipulation. [1] Gorb S. Functional surfaces in biology: mechanisms and applications. CRC Press; 2006. p. 381-97.

Water droplets are commonly found in our natural environments, e.g., from rain droplets to fog and cloud formations. Understanding the interactions between water droplets and engineered surfaces is essential for many industrial processes and applications, including water and fog harvesting, water desalination, and waste water treatment. One effective way of understanding these interactions is to study how natural surfaces can manipulate tiny water droplets, as these surfaces have evolved to deal with water in their everyday lives. In this talk, I will showcase a number of biologically inspired materials developed in our laboratory that can help efficiently acquire water from thin air, as well as reduce waste water generation from various industrial and household activities. Some of these bioinspired materials may help resolve one of the engineering grand challenges in enhancing water sustainability in many areas of the world.

Surface patterns that are responsive to mechanical stimuli are useful for designing functional materials with tunable wetting properties. One simple bioinspired method to realize such texturing is by wrinkling stiff skin layers bonded to pre-strained elastomeric substrates. Wrinkling as a general platform for mechano-responsive systems, however, has been limited by the formation of cracks at random locations in the skin layer under applied strain. Cracks are detrimental for creating surfaces with designed wetting properties where controlled structural features are important. In this work, we present a crack-free wrinkling system where the surface topography can be dynamically tuned under mechanical strain. A soft, fluoropolymer skin layer deposited on PDMS via a CHF3-plasma treatment achieved more than a 10-fold increase in the amount of pre-strain that could be relieved without cracking compared to conventional, hard skins, which offers a wider range of tunability over wrinkle wavelength and amplitude in a crack-free regime. Furthermore, the orientation of wrinkles could be modulated under cycles of stretching and releasing without cracks or delamination. Taking advantage of soft-skin-based wrinkles, we demonstrated switching of anisotropic water spreading that has not been possible with the traditional wrinkling systems. With exquisite control over external strain and starting wrinkle geometries, our crack-free, soft materials systems will have positive implications for controlled superwettability, adhesion, and directional water transport.

For the light-driven motion on the surface of liquids, various strategies have been utilized for faster motion and special applications such as cargo delivery or liquid fluid drag researching. Among various efforts that have been reported to propel the motion at interface, Marangoni effect induced by temperature gradient plays dominant role in providing the propulsion. Marangoni effect, however, could not provide enough propulsion in the liquids with lower surface tension such as water with the addition of surfactants. In this presentation, we will discuss a new propulsive mechanism that is enabled by the generation of vapor rather than Marangoni effect. Such mechanism, independent of the surface tension, allows the broad application of motors under various liquid conditions including liquids with low surface tension. In the biological process, such as the natural water transpiration of leaf, plant leaves with hydrophilic surfaces evaporates rapidly to reduce the growth of micro-organisms under solar light irradiation. During the evaporation, the water on the hydrophilic surface can be spread out and continuously replenished through the numerous micro-pores within the leaf. Such hydrophilic evaporative system takes advantage of the phenomenon of localized heating and presents the outstanding evaporation performance with largely reduced thermal loss. Inspired by the natural leaf transpiration, a bioinspired floating paper coated with assembled plasmonic nanoparticle film (PGF-motor) was fabricated to harvest incident light energy and convert into localized heat. The converted heat prompted fierce vapor generation and provided the driving force that propelled the motion of PGF-motor. With this new driving mechanism, the motion of the PGF-motor on the surfaces of various liquids such as organic solvent with different surface tension, viscosity or boiling point and the directional control was also demonstrated. A new design by collecting and confining most of generated vapor from PGF-motor within the confined space also led to significantly increased motion speed.

Many superhydrophobic surfaces show a self-cleaning effect. Dust particles, adhering to the surface, are washed off by water drops. This self-cleaning effect keeps many biological surfaces such as leaves of the lotus plants free of dust. For artificial surfaces contamination by oily substances, however, limits the duration of the effect. One step towards self-cleaning also of organic contamination is to use metal-oxide photocatalysts (MOPCs) such as TiO2, ZnO, SnO2, CeO2, Ag2O, Fe2O3, WO3, and V2O5. They create reactive free radicals by generating electron-hole pairs under light irradiation. This photocatalytic activity causes oxidation or decomposition of most organic molecules and leads to several secondary reactions. We demonstrate how MOPCs can be coated in a simple way with a stable brush of polydimethylsiloxane (PDMS). The hydrophobic surfaces remain photocatalytic active. Superhydrophobic wetting properties are realized by grafting PDMS on hierarchical-structured MOPCs. Therefore, the superhydrophobic PDMS-MOPC surfaces combine self-cleaning properties with chemical degradation of contaminants. PDMS-coated MOPC nanoparticles can also be dispersed in non-polar organic solvents. Furthermore, to create photocatalytically active lubricant impregnated surfaces we infused mesoporous PDMS-coated-TiO2 with silicone oil. Liquid drops such as water, methanol and even low surface tension fluorocarbons, slide on the surface with tilt angles below 1°.S. Wooh, N. Encinas García, D. Vollmer & H.-J. Butt, Adv. Materials2017, 29, 1604637.S. Wooh & H.-J. Butt, Angew. Chemie Intl. Ed. 2017, 56, 4965.

Nature provides inspiration for self-cleaning surfaces such as the lotus leaf. To design such surfaces, it is known that we need to combine some rough structures with low surface energy materials. Inspired by biomimetism, we will study the effect of surface disorder on superhydrophobicity. Our results, quite generally, prove that introducing disorder, at fixed given roughness, will lower the contact angle: a disordered substrate will have a lower contact angle than a corresponding periodic substrate. We also show that there are some choices of disorder for which the loss of superhydrophobicity can be made small, making superhydrophobicity robust.Moreover, we will consider recent wetting literature devoted to the Lotus effect reviewing in particular the fabrication techniques. More recent results about robust superhydrophobic surface treatment will be presented for the first time.

Graphitic carbons have many important applications including electrodes, adsorbents, catalyst support, and solid lubricants. Since the water-graphitic interface is essential to these applications, understanding the interaction between water and graphite is critically important for both fundamental material characterization and practical device fabrication. Recent research interests in graphene and carbon nanotubes over the past decades have brought renewed interests in the water wettability of graphitic carbons. Since 1940s, the prevailing notion on this topic has been that graphitic carbons are hydrophobic, which is supported by many previous water contact angle tests and very well accepted by the community since sp2 carbon is non-polar in nature. However, the recent results1 from our groups showed that graphitic carbons are intrinsically mildly hydrophilic and adsorbed hydrocarbon contaminants from the ambient air render the surface to be hydrophobic. This unexpected finding challenges the long-lasting conception and could completely change the way graphitic materials are made, modeled and modified. With several other research groups reporting similar findings, it is important for the community to realize the importance of airborne contamination on the water wettability of graphitic materials and revisit the intrinsic water-graphite interaction. This presentation aims to summarize our recent work1, 2 on the water wettability of graphitic carbons and discuss future research directions towards understanding the intrinsic water-graphite interaction. Historical perspective will first be provided highlighting the long accepted notion that graphite is hydrophobicity along with a few reports suggesting otherwise. Next, our recent experimental data will be presented showing that pristine graphene and graphite are mildly hydrophilic; FTIR, XPS and ellipsometry characterization showed that hydrocarbons adsorb onto the clean surfaces thus rendering them hydrophobic. These results are further rationalized by analyzing the change in surface energy of the graphitic surfaces before and after hydrocarbon contamination. Then the effect of defects of graphite and the testing methods, e.g., advancing, receding and static contact angles, will be discussed. Lastly, consequences of these findings and future research directions to address a few important unanswered questions will be discussed.

After a review of portions of our research on wetting and superhydrophobicity, the use of several of the concepts of this work will be described. Several series of experiments involving contact line pinning will be discussed that were designed using the contact line perspective of wetting and require this perspective to explain the observed results. Perspectives based on contact areas, for example, Wenzel’s and Cassie’s, are not useful in these experimental situations. Descriptions of using thin hydrophilic contact lines to support films of water (puddles and kinetically trapped thin films) on water-repellent surfaces and to control the shape (both 2D and 3D) of these thin films and puddles will be presented. Dip-Coating deposition on both chemically and topographically patterned surfaces will be discussed. Water capillary bridges that span hydrophilic pinning features on parallel and hydrophobic surfaces are distorted by shearing the parallel plates at a low rate. The capillary bridges lengthen and distort to balance Laplace pressure (equilibrate mean curvature) as the features are separated and eventually rupture at a distance that is a function of the liquid volume, the advancing and receding contact angles of the surfaces, the separation between the parallel surfaces, and in particular, the shape and orientation of the hydrophilic pinning features. Sessile capillary bridge failure will be introduced and distinguished from tensile capillary bridge failure.

Unpublished recent results on jumping and bouncing drops will also be presented.

Droplets slip and bounce on superhydrophobic surfaces, enabling remarkable functions in biology and technology. These surfaces often contain microscopic irregularities in surface texture and chemical composition, which may affect or even govern macroscopic wetting phenomena. However, effective ways to quantify and map microscopic variations of wettability are still missing, because existing contact angle and force-based methods lack sensitivity and spatial resolution. Here we introduce wetting maps that visualize local variations in wetting through droplet adhesion forces, which correlate with wettability. We develop scanning droplet adhesion microscopy, a technique to obtain wetting maps with spatial resolution down to 10 µm and three orders of magnitude better force sensitivity than current tensiometers. The microscope allows characterization of challenging non-flat surfaces, like the butterfly wing, previously difficult to characterize by contact angle method due to obscured view. Furthermore, the technique reveals wetting heterogeneity of micropillared model surfaces previously assumed to be uniform.

Dynamics of drops on surfaces are important for the basic understanding of various processes, ranging from daily life to cooling and coating. Recently, lab-on-a-drop rises attentions, because various functions of traditional chemical processes can be achieved this technique. Thus, controllable behaviors of drops on surfaces are desirable. The dynamics and interactions between drops and the superhydrophobic surface have been intensively studied in recent years. Various kinds of interactions, including rebounding, jumping, self-clearing, and cooling have been reported. Controlling the interaction between the drop and the solid surface is the key of these phenomena. Several studies utilizing the electric wetting have been demonstrated in hydrophobic surfaces and superhydrophobic surfaces. However, the present of an electrode within a drop may limit its applications. To overcome this problem, dielectric wetting6,7 has been proposed and realized in different conditions mainly for actuation. In this study, we show rebounding of drops controlled by electric field may be realized by dielectric wetting, which may enable new applications.1-5 In this work, Electric field effect on liquid drop rebounding is studied in interdigitated array (IDA) electrodes covered with superamiphiphobic coating under AC field. Coefficients of restitution are measured in different applied voltages. The results show that a medium voltage applied on IDA (~ 30V) can effectively change the drop rebounding on the IDA surface. We also directly measured the adhesive force curves and contact angles of drops on IDA under different voltages. The results suggest that only small fraction of the drop is tightly pinned on the surface while the other parts of the surface remain superhydrophobic. This new method of controlling liquid-solid interaction may enable new drop based microfluidic applications. A simple control of drop rebounding distance is also demonstrated.

Engineered non-wetting surfaces inspired by biological species are of interest in the industry due to their potential applications such as water repelling, self-cleaning, anti-icing, anti-corrosion, anti-fouling, and low fluid drag surfaces. However, the adoption of non-wetting surfaces in large scale industrial applications has been hampered by synthesis techniques that are not easily scalable and the limited long term stability and wear robustness of these surfaces in service. In this study, we demonstrate a simple, low cost, and scalable electrochemical technique to produce robust composite coatings with tunable non-wetting properties. The composite coatings are composed of an ultra-grain nickel matrix with embedded hydrophobic cerium oxide ceramic particles. Comprehensive characterization, including wetting property measurements, electron microscopy, focused ion beam analysis, hardness measurements, and abrasive wear testing were performed to establish the structure-property relationships for these materials. The grain refinement of the nickel matrix contributes to the high hardness of the composites. As a result of the bimodal CeO2 particle size, hierarchical roughness is present on the surface of the composite, leading to remarkable non-wetting properties, even after 720 m of abrasive wear.

8:00 PM - BM10.03.03

Potential Skin Friction Drag Reduction and Vibration Control in Water-Repellent Surfaces Fabricated with Different Biomimetic Approaches

In the last years, water-repellent surfaces have been widely studied in terms of design, processing and related properties (e.g. self-cleaning, anti-icing, frictional drag reduction). Among the biomimetic approaches to their fabrication, the one inspired by Lotus leaf envisages a two-tier, hierarchical structure enabling the entrapment of air within the solid surface, which allows a Cassie-Baxter wetting state when combined with low surface energy. The so-obtained superhydrophobic surfaces (SHSs) display water contact angle (WCA) larger than 150°, usually coupled with small contact angle hysteresis (CAH). Meanwhile, the approach inspired by Nepenthes pitcher plant is based on the presence of a low surface tension liquid as outer layer filling the pores of the material surface, thus creating a liquid-liquid interface with contacting drops. The resulting Slippery Liquid-Infused Porous Surfaces (SLIPSs) usually display lower WCAs compared to SHSs but the same small CAH. In addition, many papers proved SLIPSs more efficient than SHSs in peculiar conditions, e.g. at high pressure or underwater.With the aim of assessing the potential application of SHS and SLIPS for civil and military vessels, we performed experiments in turbulent regime (Re≈106) evaluating both the frictional drag and the vibration induced by the turbulent boundary layer by means of a purposely designed setup placed on the top of a high speed channel. A floating test surface (48x28 cm2), connected to a flexural load cell (0-20 N) and aligned through a levelling screw system, allowed the measurement of the frictional force exerted by the flow over the surface. On the other hand, the vibrational response of thin plates fixed to a rigid frame was measured by 8 piezoelectric ICP accelerometers.The tested SHSs consisted of aluminum plates dip-coated in a isopropyl alcohol-based suspension of alumina nanoparticles, afterward immersed in boiling water to form boehmite AlOOH with flower-like nanostructure. To lower surface energy, fluoroalkylsilane molecules were grafted to the surface. As-produced SHSs had WCA = 164° and CAH = 6°. On the other hand, SLIPSs were fabricated via infusion of a fluorinated oil (Krytox 100, DuPont) within the pores of SHSs. SLIPSs had WCA = 121° and CAH = 4°.Drag measurements over random textured SHSs confirm the surface roughness as key parameter: the simultaneous air plastron monitoring clearly reveals that the lack in drag reduction is linked to an early air loss, only partially hindered by increasing the roughness (from 1.5 μm to 4 μm) via sandblasting. Meanwhile, on SLIPSs a drag reduction of 10-16% is observed across the tested flow velocity range (1.0-3.5 m/s).Moreover, the analysis of the vibrational response shows a clear trend of SLIPSs at reducing the acceleration response in a quite large frequency range and up to 4 m/s. On the contrary, SHSs seem to induce a higher vibration level most likely due to the continuous plastron modification.

This paper shows the experimental results obtained using a biomometic nano-coating applied to theslippers of an axial piston pump, to reduce the friction losses in order to improve the pump overall efficiency. The needto provide, especially at low rotational speed, hydrodynamic lift, causes power losses, in terms of volumetric andmechanical efficiency, due to the contrasting need to increase leakage to provide lubrication and to keep a minimumclearance in meatus to limit the volumetric losses. The application of special surface treatments have been exploitedin pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers,but the potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has neverbeen exploited. The present work is based on the structural modification of surfaces by deposition of hybrid layers,obtained by wet synthesis and made up of ceramic oxide nanoparticles coupled with a fluoroalkilsilane (FAS) on aslipper made of a CuZn40Al2 alloy. The working fluid used for the experimental tests is a mineral oil. Theperformances of these surfaces, were investigated in a dedicated test rig, simulating the normal working conditionsand the results here presented. The used samples were also studied after the tests in order to investigate thedurability performances of the nano coating. Thanks to the surface functionalizzation the behaviour of the testedcomponent drastically changes from oleophilic(static contact angle 16,7°) to oleophobic (static contact angle 123,8°)and the friction coefficient has been reduced of more than 20%.

Slippery liquid-infused porous surfaces (SLIPS) are a biomimetic form of non-wetting surface that consist of a film of lubricating liquid infused in a porous substrate. The infusing liquid can be engineered to repel most any impinging liquid, making these surfaces ideal for drag reduction at boundary layers. The use of SLIPS in the harsh conditions commonly occurring in combustion fuel delivery could reduce coking build-up and enhance heat transfer through reduction of the stagnant boundary layer. However, at elevated temperatures, common infused liquids can degrade or volatilize, exposing the substrate and reducing the effectiveness of the surface. To design SLIPS for high temperature applications, infused liquids need low volatility and high degradation temperatures. Ionic liquids meet these criteria but have relatively high surface energies, which can cause displacement of the ionic liquid when a lower surface energy liquid, such as hydrocarbon fuel, is introduced. Maintaining a stable SLIPS structure is a delicate balance of interfacial energy. However, with proper chemical design, an ionic liquid can be imbued with paramagnetic susceptibility, which allows application of an external magnetic field to force preferential infusion of the ionic liquid and overcome the energy imbalance. Here, we present the first use of neat paramagnetic ionic liquids as infusing liquids in high-temperature capable SLIPS devices. While subject to a magnetic field, lower surface energy hydrocarbon-based fuels are prevented from displacing the infused liquids. The customizability of ionic liquids yields the ability to independently tailor magnetic susceptibility and surface tension to meet application requirements. Synthesis and characterization of a range of novel paramagnetic ionic liquids are detailed and distinctive SLIPS behavior is demonstrated with these magnetically-responsive, infused systems.

In various industrial fields including heat pump systems and aircrafts, ice formation on surfaces can yield drastic losses. Decreasing ice adhesion strengths of surfaces has been highlighted since it has the potential to enhance energy efficiencies of target applications by minimizing wasted energy for defrosting. Recently, many studies have successfully decreased the ice adhesion strengths of surfaces by forming superhydrophobic nano/microstructures on target surfaces. Although they have demonstrated successful decrease in ice adhesion strengths of target surfaces, the nano/microstructures still needs characterization and optimization in terms of their shapes to further reduce the ice adhesion strength of surfaces. Inspired by bush cricket, we report that the surface patterning with structures of low aspect ratio, which is defined as a ratio of height to width, can effectively reduce the adhesion of ice. We further developed the scalable fabrication method to form micro-scale patterns with low aspect ratios on aluminum surfaces by using chemical etching method and subsequent coating with a low surface energy material. As a result, compared to bare aluminum and control planar surfaces, the ice adhesion strengths of the newly developed surfaces decreased by about 90% and 70%, respectively. Importantly, the low ice-adhesive aluminum surfaces had good durability under the repeated ice adhesion test. Moreover, this simple method can be applied to curved or large-scaled surfaces for its simplicity. The developed surface has the potential to improve energy efficiency of the equipment with no additional system.

AcknowledgementThis research was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20164010200860).

Plant-derived polyphenols have been widely used to design new multifunctional materials for particle and surface modification. However, lack of temporal and spatial control over the oxidation and deposition process limits the usage of this diverse class of natural compounds. Uncontrolled autoxidation and deposition of phenolic compounds begins as soon as a solution is exposed to basic pH. In this project, inspired by functional properties of natural antioxidants, capable of scavenging free radicals and reactive oxygen species (ROS), we have developed a method to effectively control the autoxidation and deposition process of nine plant phenolic compounds under basic conditions by using sodium ascorbate (SA), glutathione (GSH), and uric acid (UA) as ROS scavengers. UV irradiation has been used as a ROS generation tool. We show that by UV irradiation of the phenolic solution containing natural antioxidants through a photomask, 2D patterns of phenolic coatings can be made in basic pH on flat substrates, or inside microfluidic channels. Post-modification of polyphenolic coating with 1H,1H,2H,2H-perfluorodecanethiol or alkyl amines makes it possible to tune wettability of the surface. We show that by functionalizing a gradient polyphenolic surface with hydrophobic groups, a gradient of wettability can be generated. UV–Vis spectroscopy, electrospray ionization mass spectrometry, and cyclic voltammetry analyses are used to investigate the oxidation of plant phenolic solution at pH 8.0, stored in dark or under UV irradiation in the presence of antioxidants. Formation of polyphenol coatings on the surface and surface chemistry after post modification have been studied using water contact angle measurements, atomic force microscopy, time of flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy (XPS). In addition to temporal and spatial control over oxidation and deposition processes in basic pH, by using antioxidants more homogenous polyphenolic coating can be formed, which may expand the scope of applications of these facile and structurally diverse natural materials in healthcare and material science application.

8:00 PM - BM10.03.08

Design and Fabrication of Superhydrophobic, Ice-Phobic Coatings for High Voltage Power Lines Application

The formation and accretion of ice on high voltage (HV) power lines components represent a huge problem which can affect the efficiency of current conduction whose removal requires expensive and time-consuming treatments. Strong snowfalls can often involve severe drawbacks such as extended blackout and damages to the HV systems due to the accretion phenomena and the subsequent breakup of the lines.Superhydrophobic surfaces (SHSs) have been widely investigated for many applications but the correlation with icephobic performance has not been clearly highlighted yet, notwithstanding many recent papers on the subject (Liu et al, Nanomaterials 2016; Kim et al, ACS Nanoorg 2012).Water repellence depends on surface chemical composition and morphology. Coupling hierarchical micro-nanostructure with a very low surface energy, a stable Cassie-Baxter state is reached preventing water drops from wetting the surface.In this work, 50 cm-long aluminum conductors commonly used in HV lines were functionalized by dip coating into a ceramic oxide nanoparticles suspension, synthesized by sol-gel route, and chemically modified with fluoroalkylsilane (FAS) solution to obtain SHSs by the typical Lotus leaf approach. In addition, some more water-repellent conductors were fabricated by infusion in a fluorinated oil (Krytox 100), according to the so-called SLIPS approach.Both the design approaches provided materials with high dynamic performances (contact angle hysteresis < 10°), while the infused samples showed a static water contact angle of about 120°, much lower than 170° reached by SHS samples. However, the advantage of Krytox as outer layer lies in the greater homogeneity of the coating, with a decreasing of local defects, this circumstance being very relevant on local interaction between the liquid and the surface .As known from the literature, substrate roughness plays a key role in superhydrophobic properties, this parameter being linked with the icephobic behavior as well (Susoff et al, Applied Surface Science 2013; Fu et al, Applied Materials Interfaces 2014).To better understand the influence of roughness on nucleation and accretion of the ice, the functionalization was performed on smooth (Ra = 0,3 μm) and sandblasted (Ra = 3.6 μm) conductors, either by SHS or SLIPS approach.Treated samples were exposed outdoor during winter at the RSE test facility located in the west of Italian Alps, at an altitude of 959m asl. SHS conductors, under particular snowfall events and conditions, showed a significant delay (some hours) in snow deposition if compared to the untreated and SLIPS ones. This effect was noticed only on sandblasted samples, while smooth SHS conductors exhibited the same behavior of untreated and SLIPS surfaces, with an easy deposition and fast accretion of the snow layer during the atmospheric event.

There is no doubt that ice is one of the most important reasons for lots of catastrophic and critical failures in the winter seasons. Ice can be observed on almost anywhere in our planet and has been the cause of failure in aircrafts, wind turbines, ships and power lines. Traditional deicing methods are extremely time-consuming, expensive and in some cases is not applicable or even can damage the surface. Recent advances in the superwetting surfaces have encouraged scientists to develop and improve different approaches to create surfaces with low ice adhesion and anti-icing properties. [1, 2]In this study, we synthesized and functionalized silica nanoparticles in a controlled approach to optimize porosity and particle size. We prepared thin films by layer-by-layer technique using polyelectrolytes and silica nanoparticles with different particle sizes. Then we encapsulated fluorinated compounds inside the films to achieve ice-phobic properties on the surfaces. In order to evaluate the mechanical properties and the ice adhesion strength, we designed a custom-built setup to simulate ice formation in nature and formed ice with a specified structure and surface area on the surface of the ice-phobic films. We applied shear and tensile tests to detach ice from the surface using a modified mechanical testing equipment with a high repeatability. The effect of the icing-deicing cycles and ice detaching on the surface of the thin films were also investigated. Thin film surfaces have been further assessed by optical profilometer, scanning electron microscope and atomic force microscopy to observe the thickness, roughness, and morphological features. It is observed that especially custom design mechanical testing setup was quite effective to study ice adhesion properties and has advantages of simple installation, high repeatability, and reliability of results. In conclusion, we proved that these new thin film coatings offer reduced ice adhesion strength and showed that their durability in icing-deicing cycles is acceptable.

Silicone is commonly used for blood-contacting medical devices; however, its hydrophobicity makes it susceptible to protein adsorption and subsequent thrombosis. Therefore, strategies for hydrophilization of these surfaces are expected to increase protein resistance, potentially improving device lifetime. Hydrophilic poly(ethylene oxide) (PEO) is known to impart exceptional protein resistance when grafted onto model surfaces such as glass or gold. We have shown that traditional PEO-silanes, when used in the bulk modification of silicones, are ineffective surface modifying additives (SMAs) as the PEO is unable to effectively migrate to the surface-biological interface. Alternatively, we have developed PEO-silane amphiphiles that, when blended into silicones, have a high capacity to undergo water-driven surface restructuring and present a highly wettable, PEO-rich surface for protein resistance. The amphiphile includes a hydrophilic PEO segment, a flexible, hydrophobic oligo(dimethyl siloxane) (ODMS) tether, and a reactive triethoxysilane (TEOS) group: α-(EtO)3Si(CH2)2-ODMS13-block-(PEO8-OCH3). In this study, a series of amphiphile concentrations [5 – 100 µmol/g medical-grade RTV silicone (MED-1137)] were evaluated as SMAs in silicone for protein resistance with a single fibrinogen solution. Additionally, surface hydrophilicity was assessed throughout prolonged exposure to an aqueous environment. Modified silicones with amphiphile concentrations as low as 10 and 25 µmol/g MED-1137 showed increased hydrophilicity and a substantial reduction in fibrinogen adsorption compared to an unmodified control. After 2 weeks conditioning, the 10 µmol/g MED-1137 samples still exhibited resistance to fibrinogen adsorption, but had slightly reduced water-driven surface restructuring. Likewise, the 25 µmol/g MED-1137 samples showed resistance to fibrinogen adsorption, post-conditioning; however, these samples were better able to sustain water-driven surface restructuring. To better discern between the 10 and 25 µmol/g samples for long-term surface hydrophilization and thromboresistance, current testing is being done with human plasma and whole blood to evaluate fibrin clot formation. Future work will involve testing these modified silicones in a dynamic, microchannel system to assess hemocompatibility under flow.

8:00 PM - BM10.03.11

Improving Superhydrophobicity of PVDF Electrospun Materials Using a Surface-Segregating Copolymer

Superhydrophobicity is controlled by both surface chemistry and surface roughness and morphology. Electrospinning creates highly porous mats composed of nanometer to micrometer scale fibers. When hydrophobic polymers are electrospun, superhydrophobic mats can be created. However, the superhydrophobicity of such materials can be enhanced through the rational design of functional, self-organizing polymers that segregate to the fiber surface. This can enable us to both control the surface chemistry and wettability of the electrospun material and tune the mechanical properties of the mat. In this work, we designed a specialty copolymer that enhances the mechanical properties and hydrophobicity of fibers electrospun from its blends with poly(vinylidene fluoride) (PVDF). We synthesized this random copolymer, poly(methyl methacrylate-random-1H,1H,2H,2H-perfluorodecyl methacrylate) (PMMA-r-PFDMA), and prepared electrospun mats from its blends with PVDF. The fiber mats prepared at different compositions and electrospinning conditions were investigated using scanning electron microscopy, dynamic mechanical analysis (DMA), contact angle, and oil/water separation experiments. The highly fluorinated side groups of PFDMA segregate to the fiber surface and enhance the surface hydrophobicity of the fibers. PMMA segment in the copolymer is known to be miscible with PVDF and thus prevents macroscopic phase separation of the blend. The interaction between the copolymer and PVDF also changes the thermal properties (glass transition and degradation temperatures) and crystallinity of the fibers. When appropriate copolymer/PVDF ratios are used, mats with better mechanical properties with improved modulus and toughness are obtained. Fiber mats containing the copolymer have increased contact angles and exhibit the superhydrophobicity. The mats are promising for various industrially important applications, such as the separation of oil/water mixtures through their selective wettability.

Strain recovery in shape memory polymers may be utilized at the micro scale to fabricate switchable surfaces. Thin film thiol-ene acrylate thermoset polymers were patterned via photolithography and reactive ion etching (RIE) to create a micron scale pillar array texture. The pillars have a conical shape due to the RIE etching in an isotropic fashion. The surface texture can be deformed at elevated temperatures, while it is in the rubbery state, to a near flat shape with the appropriate pressure and cooled down to room temperature to lock in this position. Upon reheating above the glass transition temperature, the pillars return to their original shape. This allows a surface to reversibly switch between two micro texture geometries. The glass transition temperature can be tuned by altering the cross-link density and polymer chain flexibility. The pillar geometry can be controlled to create a structures that create a superomniphobic surface (superhydrophobic and superolephobic). After deformation, the surface loses its superomniphobic properties making it more wettable. It was found that strain recovery in micron scale shape memory polymer allows deformed pillars to return to their original shape making it possible fabricate surfaces that can reversibly switch between two wettable states.

Titanium oxide is well known biocompatible material besides its application in different diverse fields. Its coatings are generally applied on body implants to prevent adverse biological effects and different substrates (Si & quartz) coated with thin titanium oxide film are used for different biological studies and development of some biosensors. Large numbers of research articles are available on these studies. Properties of titanium oxide thin film are modified by process parameters and/or incorporation of dopants in to the films. What actually these dopants at micro or nano level in the TiO2 to change its biological property is still an issue to be explored in more depth. It has reported by some authors that it is surface morphology of the film which is responsible for biological properties of the surface where as other group of researchers rely on work function of the dopant atom to justify the role of dopant in titanium oxide film. Conflicting results appear in the literature. Being a very important issue we tried to enhance the understanding this topic.The glass substrates coated with thin films of TiO2 undoped as well as doped with Pd, La and Ru. We studied biological carried out biosensor response properties using different enzymes adsorbed on the surface these substrates. Large variation in properties exhibited by these substrates has been observed. Various Metal Pd, La and Ru ion doped TiO2 nano-structured films shows super hydrophilic surface to immobilize the enzyme on the film surface for efficient biosensor electrode application. Various metal ion doping creates greatly oxygen deficiency on nanostructure TiO2 films which leads to make super hydrophilic surface to load the enzyme efficiently onto the film surface. It is efforts to link the observations to the nature of dopants and surface morphology of the substrate at micro/nano level. XRD, SEM and AFM investigations of all the substrates have been carried out and other investigations done by XRD, XPS to draw conclusion regarding oxygen deficiency onto the film surface to support these findings.

Highly precise self-assembly of nanomaterials in the ink droplets along the vapor-solid-liquid three phase contact lines could be accurately achieved.[1] Significantly, the basic units (dot, line, plane and stereo structures) via the printing technology can be precisely controlled.[2] We achieved the silver nanoparticles assembled conductive patterns with single nanoparticle resolution.[3] Based on the manufacturing of functional nanomaterials and controllable spreading and transferring of liquid droplets, we fabricated the superoleophilic patterns on the hierarchically structured superhydrophilic plate by ink-jet printing.[1] Thus the image area and non-image area can be achieved on the plate, which can be directly used as the printing-plate.[4] Our further work on assemble metal nanomaterials or colloidal nanoparticles via feasible printed process, patterned the various linear or curves 1D/2D morphologies and optimal interconnects on diverse substrates.[5] The desirable conductive patterns contribute the remarkable application on sensitive electronical skin[5a], transparent touch screen[5b,c], multi-layer circuits[5d], ultra-integrated complex circuits[5e] and soft actuators[5f], as well as high performance photonic crystal sensors[6]. These achievements on functional printing are derived and benefited from the fundamental researches on solid/liquid interfacial wettability manipulation, morphology control of dried ink droplets, as well as functional nanomaterial fabrication, which develop the research system of Green Printing Technology.

Droplet manipulation on super-repellent surfaces (i.e., surfaces that are extremely repellent to liquids) has been widely studied because droplets exhibit high mobility, minimal contamination and minimal sample loss. Various droplet manipulation methods including, electric fields,magnetic fields, tracks, and wettability gradients have been developed for manipulating droplets of water (a liquid with high surface tension) on superhydrophobic surfaces (i.e., surfaces that are extremely repellent to water). However, superhydrophobic surfaces cannot repel low surface tension liquids. Consequently, superomniphobic surfaces (i.e., surfaces that are extremely repellent to virtually all liquids) are necessary for manipulating droplets of both high and low surface tension liquids. To the best of our knowledge, there are no reports of dropletmanipulation methods that utilize superomniphobic surfaces to sort droplets with a wide range of surface tensions using a single device.In this work, we synthesized tunable superomniphobic surfaces with fluorinated, flower-like TiO2 nanostructures. We demonstrate that the surface chemistry, and consequently the solid surface energy and contact angle hysteresis (i.e., the difference between the advancing[maximum] and receding [minimum] contact angles), of our superomniphobic surfaces can be tuned using UV irradiation. This allows us to systematically tune the mobility of droplets with different surface tensions on our superomniphobic surfaces. Leveraging the tunable mobility of droplets on our superomniphobic surface, we fabricated a simple device with precisely tailored solid surface energy domains that, for the first time, can sort droplets by surface tension. Our devices can be fabricated easily in a short time and each device can be reused to sort droplets by surface tension. Further, our devices can be readily used to estimate the surface tension of miscible liquid mixtures that in turn enables the estimation of mixture composition. This is particularly useful for in-the-field and on-the-go operations, where complex analysis equipment is unavailable. We envision that our methodology for droplet sorting will enable inexpensive and energy-efficient analytical devices for personalized point-of-care diagnostic platforms, lab-on-achip systems, biochemical assays and biosensors.

Wettability is a feature of a surface that characterized his ability of being wetted or not by different kinds of liquids. This feature is a synergistically dependent of both the surface chemistry and morphology. Tuning the wettability of a surface requires a fine control of these two parameters, which is still a challenging research topic, especially if one want to be able to control the wettability of whatever kind of surface. For solving this last point, surface functionalization methods should be used. These methods may be used in order to change the morphology of a surface, its chemical properties or both.Our group developed different techniques that allow us to functionalize almost all kind of surfaces: transparent materials, fragile materials … One of this method is based on nanospheres lithography. Thanks to a coating of spherical nanoparticles, we can change the morphology of the surface and the chemistry (i.e., the chemistry depends of the material of the nanospheres). The chemistry may also be tuned after the deposition of the nanospheres by coating them with a desired material. Moreover, if the diameter of the nanospheres is lower than the wavelength of visible light, such kind of coatings may be transparent. As example, superhydrophilic surfaces based on the use of polystyrene nanospheres coated with TiO2 and TiO2/SiO2 mixture will be presented. We can also use nanowires to functionalize a surface. Once again, the chemistry of the functionalized surface may be tailored by a proper coating.As explained previously, by varying the material of the coating we can drastically change the behavior of our surface. As example, we will show how a superhydrophilic surface is converted in a superhydrophobic one. This is a proof of the versatility of our methods which allow us to do superhydrophilic or superhydrophobic coatings on almost all surfaces.

9:45 AM -

BREAK

10:15 AM - *BM10.04.04

The DAGS-Chemistry—Droplet Assisted Growth and Shaping for Synthesis of Polymeric Nano- and Microstructures

The synthesis of nano and microstructures are an emerging field in chemistry and materials science. They can be made from a large variety of materials, for example metals, semi-metals, or polymeric substances. Usually, these particles exhibit a comparable simple shape, for some are high temperature is required and for many (except polymers) of them no covalent bonds are formed during formation /1/.Some years ago, we have presented the synthesis of silicone nano filaments in particular for coatings delivering superhydrophobic, superoleophobic, or superamphiphobic surface properties /2, 3/. Also, nano- and microstructures different from filaments have been synthesized in a reproducible manner /4/.Recently, we have shown a reaction mechanism, explaining how these one-dimensional growths take place /5/. Based on this new scheme we are able to synthesize silicone nano- and microparticles of different shapes depending on the reaction conditions. Some of these structures exhibit a shape complexity which goes clearly beyond wires and filaments. The mechanism of this synthesis is applicable not only to silicone structures but also to other chemical compounds, for example germanium oxide.In this presentation, we will give an overview about this novel synthesis scheme which we call “Droplet Assisted Growth and Shaping” (DAGS) approach. Applying appropriate reaction conditions allows for the directed growth of nano- and microstructures of complex shape. We believe that this reaction scheme is very promising in chemical synthesis and material science, since it enables us to form complex nano and microstructures from polymeric materials at room temperature in aqueous medium.References:SC Glotzer, MJ Solomon, Nature Materials 6, 557G. Artus, S. Jung, J. Zimmermann, H. P. Gautschi, K. Marquardt, S. Seeger, EP1644450A2 (2003), Adv. Mater. (2006),18, 2758J. Zhang, S. Seeger, Angew. Chem. (2011) 50, 6652Stojanovic, S. Olveira, M. Fischer, S. Seeger, Chem. Mater. 2013, 25, 2787G Artus, S Olveira, D Patra, S Seeger, Macromol. Rapid Comm. 2017, 38, 1600558

There are a lot of functional surfaces in nature, for instance, superhydrophobic surface of lotus leaves and adhesive superhydrophobic surfaces of rose petals. There are various artificial superhydrophobic surfaces have been reported, however, those built on brittle and fragile materials’ surface, so that those are difficult to transform their surface structures. In this study, we have focused on vulcanized rubber, and attempted to prepare flexible and deformable superhydrophobic rubber surfaces by simple vulcanizing pressing with finely patterned molds. An unvulcanized rubber sheet containing carbon black, sulfur, and so on, was put on single crystalline silicon (Si) molds, which has hexagonally arranged micron scale hollow array structures prepared by lithographical technique. Then the unvulcanized rubber sheet was pressed 5 MPa and heated at 180 oC for 10 min to vulcanize rubber. After vulcanization, the vulcanized rubber sheet was peeled off from the Si mold. The surface structures were observed by using a laser microscope, and surface wettabilities were measured by using water contact angle (WCA) analyzer with 1.5 µL purified water. According to the surface observation by a laser microscope, the rubber sheet surface had fine arranged spiky structures, which are inverse structures of the Si mold hollow array. The spiky vulcanized rubber surface showed superhydrophobicity, and WCA was more than 158o. Generally vulcanized rubbers have a repeatedly stretchable property. So, when microstructured rubber sheet was elongated, their spike-arrangement was transformed from hexagonal to linear arrangements without spike height changes. We assumed that spike areas acted as thick rubber layers and other area acted as thin rubber layer, therefore, thin rubber area preferentially elongated. It might be a reason why spike heights did not change. Superhydrophobicity was still remained after stretching the microstructured rubber surfaces. These results indicated that we can dynamically re-design microstructure arrangements which determines superhydrophobicity and, in addition, other functions can be added by changing the design of microstructure arrangements.

11:00 AM - BM10.04.06

How Different Bioinspired Nanostructures with Superwettability Affect Bacteria Adhesion and Biofilm Formation

Titanium (Ti) and its alloys have been extensively used in biomedical devices and surgical implants due to their excellent mechanical properties and biocompatibility. However, the short and long term performances of these Ti-based medical devices can be adversely affected by the growth of bacteria that can cause infections and inflammations of the surrounding tissue. A lot of bioinspired surfaces with superwettability have been fabricated to inhibit bacteria attachment and biofilm formation. However, it is often questionable if such anti-fouling effects may be sustainable.

In this study, different bioinspired nanostructures (i.e. nanopillar-type and pocket-type) were fabricated on titanium surfaces. Both nanostructures have shown superwettability. It has revealed that the pocket-like structure attracts more bacteria to attach but exhibits highest anti-microbial efficiency compared to both nanopillar-structure and polished surface. For the nanopillar structure, it can delay biofilm formation but it cannot achieve sustainable anti-biofilm performance. However, it has demonstrated that the pocket-type nanostructured titanium surface has the potential for sustainable anti-biofilm performance. In addition, the computational modelling developed in this work has also demonstrated that the commonly observed surface roughness effect on bacteria adhesion may not work for nanostructures such as nanopillar-like structure or three-dimensional porous structures.

11:15 AM - BM10.04.07

Development of Liquid-Like Copolymer Coatings with Tunable Liquid Repellency and Surface Patterning Abilities

Here we reported a design strategy on the surface immobilization of “liquid-like” copolymer coatings for tunable liquid repellency and surface micro-patterning abilities. The copolymer coatings showed “liquid-like” properties that common organic liquids could slide on the coated surface with extremely low contact angle hysteresis. We revealed that the molecular configuration of the “liquid-like” chains in the copolymer played a key role in the liquid repellency. Our coatings are transparency and could be applied on various substrates. Moreover, by tuning the chemical composition of the copolymers, we could further tune the repellency for a broad range of liquids, which enabled micro-patterning and transportation of liquid droplets.

Biological superwettable materials play key role in the evolvement of the biological systems during the billions of year of nature selection process. These materials are involved in various critical functions for the biological systems, including energy conversion and preservation, self-cleaning and antifouling, nutrition purification and supply, and thermal regulations. Learning from those biological superwettable materials provides an alternative approach in engineering functional man-made materials. In this presentation I will discuss our recent effort in the bioinspired superwettable materials and surfaces for energy conversion at interfaces, including the photothermal conversion at the liquid-air interfaces and also at the solid-solid interfaces. The key design for the photothermal conversion at the liquid-air interfaces involves the focus of the energy conversion process at the liquid-air interfaces. Such focus prevents the spread of the energy to the bulk of the liquid, reduces the thermal loss and leads to the increased efficiency of the energy conversion process. This presentation will discuss the design principle to meet both the requirement of the wettability and the requirement of the thermal properties. In the presentation, I will also discuss the various applications we have explored for such energy conversion at the liquid-air interfaces, such as solar-driven evaporation and steam generation, solar-driven interfacial welding of metallic nanowires, vapor-chamber based solar-energy harvesting, and multi-functional interfacial membranes for water purification and clean water generation. Besides the energy conversion at the liquid-air interface, the extension of the similar approach to the energy conversion at the solid-solid interface will be discussed at the late part of the presentation. With the rapid development of the energy conversion at the interfaces, the potential challenges in applying such approach for practical industrial applications, including the scale up of the interfacial systems, the long-term stability of the system, and the fouling issues will also be discussed at the end of the presentation.

Formation of functional coatings, which exhibit outstanding surface properties, such as super-liquid-repellency and low friction/adhesion, has generally relied on a combination of surface structures and low surface energy materials (typically long-chain perfluorinated compounds, LPFCs). However, the chemical and physical effects of the LPFCs on human health, and the environment, have been lately viewed with suspicion. In addition, once such man-made surfaces are physically/chemically degraded, they permanently lose their surface properties. In contrast to this, there are living creatures that sustain their surface properties through continuous secretion of waxes or mucus. To realize long-lasting surface functionalities, similar to those observed in nature, we have particularly focused on “syneresis” of organogels, which is the release of liquids from inner gel matrices to their outer surfaces. In this study, organogels were prepared, based on a cross-linking reaction of 2 types of polydimethylsiloxane (PDMS) with a Pt catalyst, and several organic guest fluids, which have named “Self-lubricating gels (SLUGs)” [1]. When compatibility between the low-surface-tension guest fluids and PDMS matrixes is decreased beyond a certain critical point, the guest liquids begin to gradually leach out to the outermost SLUG surfaces. By taking advantage of the syneresis behavior of these guest fluids, we can successfully achieve various dynamic/durable surface functionalities, similar or beyond those of living surfaces.For example, viscous emulsions (mayonnaise, honey and so on) can flow on our SLUG surface more freely than those on a non-syneretic gel surface. For anti-icing/snow applications, we can tune the syneresis temperature to achieve reversible thermo-responsive properties. In this case, the syneresis gradually begins as the temperature is cooled below 0 °C, and the syneresis fluids returns back into SLUGs again by heating it to room temperature. Thanks to this smart thermo-responsive property, an ice-pillar or snow on SLUGs below 0 °C can easily slide off without any external force. Moreover, we can successfully demonstrate regeneration of superhydrophobicity using n-octadecyltrichlorosilane or proryltrichlorosilane as an active guest fluid. Some of the samples can survive even after 24 hours air-plasma/172 nm-vacuum UV light exposure [2] and 1 year outdoor exposure test. Our SLUGs undoubtedly show great potential for applications in dynamic, multifunctional, and self-healing coatings and have possibilities beyond those of biological surfaces.

AcknowledgementsThis work was partially supported by Advanced Research Program for Energy and Environmental Technologies (No. P14004) from New Energy and Industrial Technology Development Organization (NEDO), Japan.

Multifunctional coatings offer many advantages towards protecting various surfaces. Silica nanoparticles are interesting owing to their high stability and interesting mechanical properties. Recently, we synthetized nanosilica particles with organic dyes immobilized inside the lattice. The aggregation induced segregation of perylene diimide (PDI) was used to control the surface structure and properties of silica nanoparticles. Differentially functionalized PDI was incorporated on the surface of silica nanoparticles through Si-O-Si bonds. The absorption and emission spectra of the resultant functionalised nanoparticles showed monomeric or excimeric peaks based on the amounts of perylene molecules present on the surface of silica nanoparticles. Contact angle measurements on nanosilca thin films showed that unfunctionalised nanoparticles were superhydrophilic with a contact angle (CA) of 0°, whereas perylene functionalised silica particles were hydrophobic (CA > 130°) and nanoparticles functionalised with PDI and trimethoxy(octadecyl)silane (TMODS) in an equimolar ratio were superhydrophobic with static CA > 150° and sliding angle (SA) < 10°. In addition, the near infrared (NIR) reflectance properties of PDI incorporated silica nanoparticles can be used to protect various heat sensitive substrates. The concept developed in this paper offers a unique combination of super hydrophobicity, interesting optical properties and NIR reflectance in nanosilica, which could be used for interesting applications such as surface coatings with self-cleaning and NIR reflection properties.

Electrically conducting polyethylenedioxythiophene (PEDOT) has been found to exhibit low intrinsic cytotoxicity and display high biocompatibility. Therefore, PEDOT films are ideal for bioelectronic-interface applications. Polymeric interfaces with optimal surface properties, such as hydrophilicity and bio-selectivity, can be controlled from various combination of functionalized monomers (EDOTs). For example, immunogenic scar formation, which insulates polymeric electrodes from targeted cells, can be avoided through biomimetic design: cell membrane-mimicking phosphorylcholine (PC)-grafted PEDOT. However, many cellular behaviors, such as migration, cannot be detected at interfaces with uniform environment and surface properties. In consideration of extending potential application of PEDOT interfaces to the research of biological activities, this work demonstrates a novel way to create polymeric interfaces with gradient surface properties.For biomedical applications, creating gradients in single-cell scale facilitates study and better understanding of various cellular response. Among many tools designed to create spatiotemporal patterns on the microscale, microfluidics has been well developed to generate chemical gradients. In an effort to transfer gradient patterns from solution to condensed matter phases, chemical reactions like etching and photopolymerization have been utilized by other research groups to create gradient surfaces. However, these approaches provided less control over the positions where reactions took place. In these methods, the serpentine channels in upstream can be etched or blocked, and thus flow patterns are unstable and time-variant. Here, we develop a device combining microfluidic and electrochemical features. With proper arrangements of electrochemical electrodes in the downstream, functionalized-poly(EDOT)-gradient surfaces are precisely controlled and electropolymerized on specified regions. The gradient patterned surface is analyzed by time-of-flight secondary ion mass spectroscopy (ToF-SIMS), with C60+ primary ion beam used to probe the surface. Phosphorous secondary ion (m/z 31.0, P-) mapping can be utilized to label the contents of PC and it shows an increasing intensity across the width of the surface, which is perpendicular to the perfusion flow direction. Mapping of nitrogen and hydrocarbon ions (m/z 14.0, N- and CH2-) provides another way to verify gradient contents of the surface. Consequently, C60-ToF-SIMS mosaic mapping and intensity profiles of the poly(EDOT-OH-co-EDOT-PC) surfaces show that the gradient pattern can be transferred from solution to the polymeric material phase through electropolymerization. The reported method and the resulting gradient surfaces with electrically conducting feature can pave a new way for in vitro cell studies, such as chemotaxis and electrotaxis.

Living organisms and biological substances are among the most difficult and persistent sources of surface fouling, particularly in medical and marine settings. The ability of organisms to adapt, move, cooperate, evolve on short timescales, and modify surfaces by secreting proteins and other adhesive molecules enables them to colonize even state-of-the-art antifouling coatings. Attempts to combat these issues are further hindered by conflicting requirements at different size scales and across different species. Our recently developed concept of Slippery, Liquid-Infused Porous Surfaces (SLIPS) provides a defect-free, dynamic liquid interface that overcomes many of these problems at once. In this talk we will present our new results showing that slippery surfaces are outstandingly effective in preventing marine fouling in both laboratory and field conditions. Detailed investigations across multiple length scales—from the molecular scale characterization of deposited adhesion proteins, to nano-scale contact mechanics, to macro-scale live observations— provides new insights into the physical mechanisms underlying the adhesion prevention. We are currently developing this strategy to solve longstanding marine fouling issues and the associated serious economic and ecological consequences for the maritime and aquaculture industries.

Lubricant infused surfaces (LIS) for fluid repellency have received significant interest in biology, microfluidics, thermal management, lab-on-a-chip, among others. While the design of LIS has been explored, efforts have focused on using empirically determined surface energies for each interface in a given system. In this talk, I discuss an approach which predicts a priori whether an arbitrary combination of solid and lubricant will repel a given impinging fluid. We validated our model with experiments performed in our work as well as in literature and subsequently, developed a new framework for LIS with distinct design guidelines. Furthermore, we show LIS with uncoated high-surface-energy solids are possible, thereby eliminating the need for unreliable low-surface-energy coatings and resulting in LIS repelling the lowest surface tension impinging fluid (butane, γ ≈ 13 mN/m) reported to date. This work suggests further opportunities for LIS in applications where other surface engineering solutions cannot be applied.

4:30 PM - BM10.06.03

How Mussels Feel about Lubricant-Infused Surfaces—Towards Understanding of Anti-Biofouling Capabilities

Liquid-infused surface coatings have shown a high capability to repel low-surface tension liquids and adhesive fluids. Their hybrid solid-liquid composition effectively shields the underlying substrate from direct contact with an external liquid phase and thus prevents fouling of the surface.In contrast to contaminating liquids that are in passive contact with a surface, living organisms such as mussels explore their environment and actively make contact with the substrate. The avoidance of attachment is therefore much more difficult. The pronounced adhesion capabilities of foot proteins secreted during the adhesion process make mussels opportunistic macro-fouling organisms that can attach to most immersed solid surfaces, leading to serious economic and environmental consequences for the maritime and aquaculture industries.Here, we explore how repellent liquid-infused coatings perform as antifouling coatings against mussel adhesion. We find that such coatings are able to mitigate mussel biofouling, with very low settlement and low adhesion strengths. In order to understand the antifouling performance against such active macrofoulers, we investigate the mussel-substrate interactions on multiple length scales. At the molecular level, we measure the deposition of mussel foot proteins on the different surfaces. At the microscale, we resolve the adhesive strength of deposited adhesive plagues and at the macro scale, we directly observe the mussel behaviour upon contact with the liquid-infused surfaces. We complement these measurements with nano-scale contact mechanics simulating the forces experienced by the mussel foot. Our investigations demonstrate that liquid-infusion considerably reduces mussel fouling via two complementary mechanisms. The entrapped lubricant deceives the mechano-sensing ability of mussels, effectively deterring the secretion of adhesive threads. Furthermore, the lubricant affects the molecular work of adhesion, resulting in reduced adhesive strength.

While various hemostatic materials have been developed, massive bleeding occurred by unexpected injury gets first aid by compressing the wound site due to the following limitations; Non cost-effectiveness of polymer-based hemostat and difficulty in coverage of the high bleeding pressure. Moreover, injuries such as fracture of cranial parts should not be physically compressed, which is likely to cause a severe brain damage. Herein, we applied diatom frustule silica as a hemostatic agent in which there is no need of physical compression for hemostasis. Inorganic hemostatic agents from diatoms, composed of SiO2 known as a relatively wettable material, were prepared by acid treatment followed by thermal annealing to remove the organic residues. Interestingly, we found that the structural difference between each species results in distinct hemostatic effect not only in vitro, but also in vivo due to the alteration of their porosity and hollow structures.

Developing drag-reducing surfaces have attracted much attention due to their potential in many applications, such as ships, underwater vehicles, and piping systems. Many studies have successfully demonstrated drag-reducing effects of micro/nanostructures, such as riblet microstructures, nanowires, and nanospheres, by containing air pocket among those structures. Albeit their successful demonstrations, enhancing the drag-reducing performance still needs further development of engineered micro/nanostructures. Here, we demonstrate the facile fabrication of a drag-reducing, superhydrophobic flexible surfaces using molding process, hydrothermal synthesis, and subsequent dip coating method. Specifically, we first fabricated the template based on denticle microstructures, consisting of a group of riblet microstructures, by mimicking the shape of shark-skin, and applied molding process over the template using polydimethylsiloxane (PDMS). Then, we synthesized the reticulated cobalt oxide nanowires with a high aspect ratio over the micro-patterned PDMS, followed by coating them with a polytetrafluoroethylene (PTFE) solution. The wettability on the fabricated surfaces showed water contact angles of 160° and sliding angles of 0.1°. Importantly, the combination of engineered micro and nanostructures significantly reduced frictional drag in high speed flow. Our fabricated surfaces are flexible enough to be attached to arbitrary curved surfaces with a curvature radius of ~1 cm. We believe that our results can provide a guideline to further enhance the drag-reducing performance of target surfaces using bio-mimetic approach.

AcknowledgementThe authors gratefully acknowledge the financial support provided by Defense Acquisition Program Administration and Agency for Defense Development of Korea (UD160013DD).

8:6 PM - BM10.07.03

Preparation of Porous Membranes with Dynamic Surface Functionality for Water Treatment

Super-wettable materials have recently attracted great interest for advanced oil-water separation. However, most of these materials are incapable of separation of emulsified oil from water because of the large pore sizes. In this study we develop a simple and inexpensive process to produce a highly porous superhydrophobic and superoleophilic membranes using polymerization induced phase separation. Butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) were in situ polymerized in presence of porogen solvents to afford a crosslinked highly porous membrane. The globule like surface structure and the alkyl groups of BMA endowed the prepared membrane superhydrophobic with static water contact angle of 155.2 ° and sliding angle of 9.2 °, and superoleophilic with underwater contact angle of 7.3° for toluene. The pore size of the superhydrophobic BMA-EDMA membrane can be readily adjusted by tuning the composition of porogens in the polymerization process, therefore enabling effective separation of water-in-oil emulsions with droplet sizes from the micrometer to the nanometer range. Surfactant stabilized water-in-oil emulsions can be separated with a permeability of 270 L/m2Lbar, high water retention (>95%) and good recyclability. Moreover, by using the dynamic UV induced disulfide surface chemistry, macro hosts such as cyclodextrin can be exchanged and renewed on the membrane surface for efficient removal of micro pollutants from wastewater.

8:9 PM - BM10.07.04

Precise Fabrication of the Bio-Inspired Phospholipid Polymer Brush Layer on Various Material Surfaces to Control the Cell Adhesion

Introduction: Surface-initiated atom transfer radical polymerization (SI-ATRP) is a promising approach to construct the well-defined polymer brushes, which can control the surface properties of original materials. The 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer brush layer, which is inspired from cell membrane surface, shows excellent properties such as antibiofouling, super-hydrophilicity and low friction. Herein, we propose the simple method to construct the poly(MPC) brush layer in a desired area on various polymeric materials for controlling the cell adhesion. In SI-ATRP, the polymerization of monomer is initiated from the surface immobilized initiator. To construct the poly(MPC) brushes on the various materials, we synthesized a novel photoreactive ATRP initiator having phenylazide groups (AzEBI). The AzEBI can be applied for various polymeric materials because the phenylazide groups form the covalent bonding with the hydrocarbon groups by UV irradiation. Furthermore, the reaction area of the AzEBI can be controlled during photoreaction. We evaluated the surface properties on the poly(MPC) brush layers initiated from AzEBI-immobilized materials.Methods: AzEBI was synthesized by the reaction between 2-hydroxyethyl 2-bromoisobutyrate and 4-azidobenzoyl chloride. The AzEBI was immobilized on the various polymeric materials by spin-coating and UV irradiation for 3 min, and then MPC was polymerized by SI-ATRP. For regulation the reaction area of AzEBI, the photo-mask with 100 mm wide line was used before UV irradiation. After SI-ATRP of MPC, the surfaces were analyzed by XPS, FT-IR, ellipsometry and static contact angle measurements. Furthermore, adhesion of HeLa cells was observed on the poly(MPC)-patterned surface.Results & Discussions: MPC was successfully polymerized via ATRP with AzEBI initiator. The thickness of the poly(MPC) brush layer grafted on the poly(ethylene terephtalate)(PET) thin film prepared on silicon substrate was 9.5 nm and the graft density was 0.25 chains/nm2. That indicated the formation of dense polymer brush layer (< 0.10 chains/nm2). The air contact angles in water on the original polymeric materials were 100°-110°, however, after grafting poly(MPC), they increased dramatically to 160°-180°. All polymeric surfaces were converted from hydrophobic to super-hydrophilic. The HeLa cells were adhered only to the original substrate area because the poly(MPC) brush layers suppressed the adsorption of cell-adhesive proteins.Conclusion: The poly(MPC) brush layers were successfully fabricated in a desired area on the various polymeric materials by regulating the photoreaction area of AzEBI. On the poly(MPC) grafting area, the surface took super-hydrophilic nature, and the protein adsorption and cell adhesion was suppressed effectively. We concluded that this technology would expand the potential application of surface functionalization of biomedical devices.

Platinum (Pt) is considered as an anti-corrosive, low immunogenic, and excellent biocompatible noble metal. For these reasons, various medical devices such as guide wires in blood vessel catheter insertion, heart pacemakers, and teeth applied materials utilize platinum. However, the wettability of platinum surface; particularly for blood-wettability in many platinum-coated medical devices has been a problem. In this study, we report a new molecule that provide good superhemophilic self-assembled monolayer on surface of platinum surfaces. The superhemophilic surface was developed by simple dipping method in 2-mercaptoethansulfonate (MES) solution during which the highly hemophile functional group, sulfonate, anchors directly onto the surface of platinum. The investigator applied 2-MES to a dental implant screw to provide superhemophilic properties, which can induce rapid in vivo healings. This method would be a good surface modification method for biomedical device made by platinum.

Engineering surface properties has been an important subject for the numerous applications of materials, and many surface modification methods have been developed using surface-active molecules or nanoparticles. When nanoparticles are used for the surface modification of polymers, their positions in polymers are critical in determining the final properties. However, engineering strategies to effectively locate nanoparticles only on surfaces have not been satisfactorily developed so far. Herein, we developed a novel surface treatment technique to efficiently embed nanoparticles only on the surfaces of polymers based on directional melt crystallization (DMC). DMC of solvent produced columnar or lamellar crystals and pore walls of Voronoi-structures. After removing the solvent crystals by sublimation, membranes of ordered pores of low tortuosity could be obtained. When a solvent having dispersed nanoparticles were applied on the surfaces of polymers, the surface-confined DMC of the dispersion produced embedded nanoparticles on the surfaces. Polyvinylidene fluoride (PVDF) was chosen as the target material because of its good thermal, chemical and electrochemical stabilities. Porous membranes of PVDF prepared by DMC techniques and commercial PVDF membranes were treated using nanoparticle dispersions. The PVDF membranes from DMC had contact angles over 140° due to the lotus effect. After the surface treatment of titanium dioxide nanodispersion, the contact angle of the membranes decreased down to 125°. Similar decreases could be found in the commercial membranes, and various parameters could influence the contact angle including contact time and treatment temperature. The structure of pore walls affected the results of liquid flux. The PVDF membranes from DMC showed excellent pure water flux results. While the commercial hydrophobic PVDF membrane had 571 LMH under 0.7 bar pressure, our PVDF membrane from DMC had 255528 LMH. After the surface treatment of titanium dioxide nanodispersion, the pure water flux of membrane increased to 282227 LMH. These membranes also showed outstanding oil-water separation ability with more than 97% separation efficiency. This surface treatment technique based on DMC is applicable to most polymers and has commercial potential since the surface properties of polymers can be tailored with using limited amounts of nanoparticles.

AbstractSpatially resolved functionalization of surfaces is important in a variety of research fields ranging from microfluidics and electronics to biotechnology. In this context, photochemical reactions have attracted much attention, because they offer both spatial and temporal control of surface modification. However, the majority of the existing methods are restricted to irreversible surface functionalization because of the formation of non-reactive covalent bonds. Here we demonstrate the UV-induced disulfide formation and disulfide reduction reactions for surface functionalization and dynamic photopatterning, which permits the light-induced attachment, exchange and detachment of functional groups on the surface.[1] We foresee that this dynamic photopatterning strategy will provide a robust tool for both the development of stimulus-responsive surfaces and for precise dynamic manipulation of interfacial properties. Furthermore, this photodynamic thiol-disulfide exchange process will provide an excellent opportunity for the design of new smart materials.

We describe a simple method to prepare oil repellent surface with inherent reactivity. Liquid-like copolymers with pendant reactive groups are covalently immobilized onto substrates via a sequential layer-by-layer method. The stable and transparent coatings showed oil repellency to a broad range of organic liquids even with the presence of reactive sites. Functional molecules could be covalently immobilized onto the oil-repellent surfaces. Moreover, the liquid repellency can be maintained or finely tailored after post-chemical modification.

8:24 PM - BM10.07.09

Liquid Transport Behaviors of Bioinspired Open Channels with Various Shapes of Micro-Sized Blades

Recently, microfluidic has attracted much attentions from due to its efficiency such as sample reduction and reaction rate improvement. However, conventional microfluidics system using closed capillary not only requires external pressures to transport liquid but also has difficult accessibility from outside inhibiting ease of cleaning and surface modification. To solve these problems, we have studied open-air micropatterned surfaces with wettability driven system inspired from nature. It is known that a lot of animals and plants in nature efficiently live using various properties derived from micropatterned surface wettability including superhydrophobic, self-cleaning, fog harvesting, and so on. Inspired materials and optimized designs contribute to development of open-air microfluidics.In our research, a coastal animal Ligia exotica which is gill-breathing but unable to swim was set as a biological model. This animal has open channels composed of numerous micron-sized blades on its legs which uptake water spontaneously to its gill driven by interfacial energy. Open channels with microstructures imitating Ligia exotica were artificially fabricated by photolithography. This open channel was able to transport water like Ligia exotica and manipulate liquid transport as we wish with controlling surface chemistry, however, it costs much to fabricate open channels by photolithography. This work aims to fabricate micropatterned channels at a low cost method which is mold process using micro triaxial scanning machine. First of all, hole array template of polyethylene substrate was fabricated by sticking of micro-sized needle or spatula repeatedly. Then, polydimethylsiloxane (PDMS) was cast on the template surface and peeled away from the template after curing. Numerous micro-sized blades like Ligia exotica were successful fabricated on the PDMS surface by mold process. The microstructures enhanced intrinsic contact angle of water into more hydrophobicity. The micropatterned surfaces modified hydrophilic by vacuum UV irradiation was able to transport water spontaneously against gravity. This work also investigated behavior of liquid transport induced by different shapes of blades, for example, liquid transport velocity, whether the cavitation occurs while liquid transport and dynamic liquid transport.

Biomimetics, the field of understanding principles abstracted from distinctive phenomenon in nature aimed at technological design and applications in human society, is a growing interest. Many bioinspired studies and technologies to control wettability, such as superhydrophobicity, self-cleaning, fog harvesting and drag reduction in fluid flow, have attracted much attentions and already been applied to industries. In our study, a coastal animal, Ligia exotica, was set as a biological model. It has pairs of hydrophilic legs on which open-air structures uptake water spontaneously to its gill using interfacial free energy. SEM observations revealed the water channels were composed of micron-sized paddle-shaped pillars oriented in parallel lines. This open-air structure has a great potential of low-energy long distance liquid transport and inter-channel liquid transport. We fabricated a series of artificial bioinspired channels on silicon wafer by photolithography mimicking the structures of legs of Ligia exotica. The channels irradiated by vacuum ultraviolet (VUV) acquire similar water transport ability with their hydrophilicity. Moreover, we found out the velocity of liquid transport in vertical direction is accelerated after a quantifiable shift of arrangement of paddle-shaped pillars although the surface area and number of the pillars in the channels are fixed. This work investigates macroscopic liquid transport on a minimum structure patterns composed of paddle-shaped pillars aligned one row in transport direction to clear the liquid transport mechanism. Also, we observed microscopic liquid spreading on several arrangement patterns of microstructures affecting the velocity of macroscopic liquid transport in terms of liquid spreading shapes, contact line advancing between two pillars, wetting on a wall of a pillar.

In this work, we reveal a reactive oil-repellent surface as a new platform for surface micro-patterning of low-surface-tension liquid precursors. Fluorescent molecules could be immobilized on the reactive oil-repellent surface by high-density and high-resolution patterning of microdroplets via a synergetic effect of droplet evaporation and condensation-enrichment. Our method demonstrated a simple approach to spatially control the surface chemistry and wettability. And we envision that our proposed surface can broaden surface functionalization for analytical and biomedical applications.

The unique surface properties of structural surfaces depend heavily on the morphology of a surface and not just chemical composition of the topmost layer. Understanding the detailed structural shape of surface is critical to surface design inspired by nature. As known, spiders and roaches have unique morphological structure of protrusion feature on its legs. The shape of protrusion features work as crucial factor to have unique surface properties. In this study, we systematically investigate the geometrical variables of protrusion and other features on the skin. In addition, the nanoscale surface morphology of the skin has been identified by using atomic force microscopy (AFM) in order to properly model and fabricate bio-mimicking surfaces. We suggest that the structural surface morphology can be a critical factor to design unique synthetic bio-inspired surface structure.

8:36 PM - BM10.07.13

Theoretical and Experimental Analysis to Make Superrepellent Surfaces with Different Tip Shape of Micropillars

We have demonstrated a structural advantage of mushroom-like micropillar arrays for making superomniphobic surfaces. We have derived and plotted theoretical graphs based on the Cassie-Baxter equation to find out an optimal condition in order to repel liquid droplet with a wide range of surface tension on a desirable surfaces. Superomniphobic experiments are carried out by using two-cases of microstructures with mushroom-like shape and cylindrical shape to compare with the theoretical analysis. The results show that only mushroom-like arrays can maintain metastable Cassie-state even with a low surface tension liquid droplet such as ethanol, which is resulted from the structural advantage of wide-tip shape of them. As a result, we have disclosed the smart function of the wide-tip structure by theoretical and experimental approaches to design superomniphobic surfaces with various potential applications.

Most living things have a surface playing a critical role in maintaining a stable internal physiological environment from thermo-regulation and tolerance of the external stimuli. This surface can be suitable under most conditions, but can’t be suitable under extreme such as high vacuum. We have reported that plasma-polymerized thin films of amphiphilic molecules (polysorbitan monolaulate; Tween 20) prevent an insect surface from evaporating water in high vacuum condition. From the result of structural analysis, it is revealed that the dense packing of molecular orientated structures in the irradiated surface produced to inhibit water evaporation from the insect body, which calls “surface shield effect”. furthemore, thermogravimetric analysis (TG) and infrared spectroscopy (FT-IR) measurements of the plasma-polymerized membrane, revealed that the insolubility of the membrane after plasma irradiation was the driving force for the formation of the intermolecular ethoxy chains of Tween 20 by plasma cross-linking .Up to date, we investigated the antioxidant and corrosion protection abilities by the surface shield effect of the plasma-polymerized thin film to use in a wide variety of biological fields for functional membranes and food packaging films. However, it was found that surface shield effect was functioned only at room temperature and low humidity, because the inner functional structures was broken under high temperatures and high humid conditions. In this research, we tried to fabricate functional thin films by plasma-polymerization of blend solutions of Tween 20 and functional molecules, such as a hydrophilic polymer material, that have a water vapor barrier property under high temperatures and high humid conditions.

Superhydrophobic surfaces submerged under water appear shiny due to a thin layer of air (‘plastron’) trapped in their texture. This entrapped air is advantageous for both anti-corrosion as well as frictional drag reduction in various applications ranging from microfluidic channels to marine vessels. However, these aerophilic textures are prone to impregnation by water due to turbulent pressure fluctuations and dissolution of the plastron into the water. Therefore, there is a need to develop mechanisms for regenerating the plastron in-situ without having to dry the surface.

In this work, we demonstrate a novel chemical method to replenish a surface plastron by using the decomposition reaction of hydrogen peroxide. It is well known that hydrogen peroxide is an unstable compound that spontaneously decomposes into water and oxygen, even at room temperature. The rate of this reaction can be increased by orders of magnitude through the use of catalysts like catalase, platinum, iodide etc (May D.W., 1901, McKee D.W., 1969, Liebhafsky H.A., 1932). We designed and fabricated superhydrophobic surfaces on silicon microposts with a catalyst (platinum) deposited within the interstices of the texture in such a way that the reaction is activated upon imbibition of the reactant/water mixture into the post array. The evolution of oxygen then re-inflates the plastron. The reaction is self-limiting, and once the plastron has been regenerated further gas generation ceases.

We use optical microscopy to observe the gas spreading in the texture as well as the development of ‘blisters’ . We also derive a thermodynamic condition for plastron recovery based on ‘hemiwicking’ theory (Bico J. et al., 2002) and validate our model using micropillar arrays of varying Wenzel roughness. We thus provide a framework for designing superhydrophobic surfaces with optimal texture and chemistry for underwater plastron regeneration. We finally demonstrate the scalability of this method by fabricating cheap and practicable surface textures on aluminum using laser engraving and deposition of a manganese dioxide catalyst thus enabling plastron regeneration on larger length scales for ocean-going applications.

Nanofabrication is an inevitable process in nanoscience and nanotechnology. Unconventional lithographic techniques are often used for fabrication as an alternative to photolithography because they are faster, cost-effective and simpler to use. However, these techniques such as nanoimprint lithography (NIL) are limited in scalability and utility because of the collapse of pre-printed structures during step-and-repeat processes. Here, we propose a new class of temperature-controllable polymeric molds that are coated with a metal such that any site-specific patterning can be accomplished in a programmable manner via precisely controlled joule-heating system. The lithography allows site-selective dewetting, sub-100 nm patterning, step-and-repeat processing and hierarchical structure generation. The programmable feature of the lithography can be utilized for the structural coloring and shaping of objects. Large-area programmable patterning, semiconductor device manufacturing, and the fabrication of iridescent security devices would benefit from the unique features of the proposed strategy.

Polyphenols are found in both plant and animal tissues, where they serve a variety of functions including mechanical adhesion, structural support, pigmentation, radiation protection, and chemical defense. The adhesive proteins of marine mussels are known to contain high levels of the o-dihydroxyphenyl (catechol) functional groups, whereas plant polyphenolic compounds containing catechol and/or trihydroxyphenyl (gallol) functional groups are widely distributed secondary metabolites with a variety of biochemical and physical functions. This talk will focus on selected catechol or gallol containing biological and synthetic polyphenols used as building blocks for multifunctional coatings. Exploiting their known interfacial adhesion properties, we have engineered a method to form thin adherent polymerized films on substrates immersed in solutions of polyphenols. Deposition is facile from an aqueous precursor solution onto a variety of solid, porous and nanoparticulate metals, ceramics and polymers. In addition to possessing inherent antibacterial and antioxidant properties, the deposited polyphenol films serve as versatile ‘primers’ facilitating secondary modifications of the primer coating such as metallization and covalent grafting of biomolecules and synthetic polymers. These coatings can be exploited for a variety of practical applications, including antibacterial, antioxidant and fouling resistant coatings on medical devices, metal deposition, plasmonic tuning and surface functionalization of nanoparticles.

8:45 AM - BM10.08.02

Self-Cleaning and Controlled Adhesion of Gecko Feet and Their Bioinspired Micromanipulators

Geckos have the extraordinary ability to keep their sticky feet from fouling while running on dusty walls and ceilings. Understanding gecko adhesion and self-cleaning mechanisms is essential for elucidating animal behaviors and rationally designing gecko-inspired devices. We report a unique self-cleaning mechanism possessed by the nano-pads of gecko spatulae in both dry and wet conditions. This study has provided direct evidence that the unique shape of nanoscale spatula pads plays a crucial role in generating robust and stable adhesion while permitting efficient self-cleaning capabilities in dynamic regimes. Inspired by this natural design, we have fabricated micro/nano-pad-terminated artificial spatulae and micromanipulators that show similar effects, and that provide a new way to manipulate microparticles in dry and aqueous environments. By simply tuning the pull-off velocity, our gecko-inspired micromanipulators, made of synthetic microfibers with graphene-decorated micro-pads, can easily pick up, transport, and drop off microparticles for precise assembling. This work should open the door to the development of novel highly-efficient biomimetic self-cleaning adhesives, smart surfaces, MEMS, tunable micro/nano-manipulators, biomedical devices, and more.

9:00 AM - BM10.08.03

Nanoengineered Surfaces with Tunable Water Adhesion Properties and Their Applications for Microdroplet Arrays

Tuning liquid-surface adhesion has attracted huge research interests due to its promising applications ranging from self-cleaning surfaces to microarrays and further.[1,2] Following Wenzel, Cassie, and Baxter, an approach to alter surface wetting properties is to introduce roughness hereon. Rough surfaces comprising nanoscale cones can easily be produced with a reactive ion etch by the one-step “black silicon method”. Tuning the etching process parameters, such as gas flow rate and etching time, allows for alternation of cone height and cone opening angle.[3]

We covered such a surface with a self-assembled monolayer of perfluorodecyltrichlorosilane to render it hydrophobic and systematically studied the macroscopic surface wetting properties as a function of the cone opening angles. The surface adhesion is found to depend critically on the cone opening angle, and can easily be tuned from highly water-repellent to complete pinning of the droplets.[4] Thus, the one-step fabricated surfaces can exhibit both the lotus effect and the rose petal effect.

The ability to tune the surface wettability opens up for a vast amount of applications, and here we develop a few related to the field of microdroplet arrays. First, we show how the microstructure-induced advancing contact angle on a rose petal surface can be exploited to create self-alignment of pipetted droplets.[5] Secondly, by superimposing the lotus effect roughness on a chemical pattern we enhance the adhesive properties to create a super-biphilic array chip. We find that such a chip in a dip-coating process will entrain droplets with sizes tunable through the dip-coating parameters. Lastly, the nanograss geometry alters the nucleation point density for vapor condensation and opens up for applications within spatial control hereof. In relation to this, we demonstrate spatial control of condensation on chemically homogeneous pillar-built surfaces.[6] Currently, the success depends on the water vapor introduction, but this restriction could potentially be depressed using spatially confined nanograss.

Understanding of the interaction between exhaled microdroplets and solid surfaces may help design antifouling materials that can prevent the transmission of microdroplets containing pathogens and hence reduce the spread of respiratory diseases. Here microdroplets from picoliter to nanoliter were successfully generated in a controlled manner to mimic the exhaled microdroplets in sneezing and coughing, which allowed us to evaluate the adhesion of microdroplets on both superhydrophobic and lubricant-infused “slippery” surfaces for the first time. We revealed the optimized condition for preventing the adhesion of microdroplets on solid surfaces.

9:30 AM - *BM10.08.05

Bio-Inspired Anti-Fogging Materials—From the Mosquito Effect to the Cicada Effect

We discuss two successive effects that generate hydrophobic anti fogging materials. (1) Scaling down the texture size on hydrophobic textured solids to nanometric scales induces a strong decrease of adhesion of hot drops deposited on such solids (mosquito effect). (2) At the same nanometric scale, modifying the shape of textures from nano cylinders to nanocones generates even more spectacular effects: adhesion becomes non measurable, and microdrops merging on such surfaces systematically depart from it (cicada effect). We discuss and interpret these effects, and then study the departing velocity and the trajectory of the expelled droplets.

Inspired by manifestations in nature, microengineering and nanoengineering of synthetic materials to achieve superior properties of many kinds has been the focus of much work. Generally, hydrophobicity is enhanced through the combined effects of surface texturing and chemistry; being durable, rigid materials are the norm. However, many natural and technical surfaces are flexible, and the resulting effect on hydrophobicity has been largely ignored. In this lecture, I show that the rational tuning of flexibility can work synergistically with the surface microtexture or nanotexture to enhance liquid repellency performance, characterized by impalement and breakup resistance, contact time reduction, and restitution coefficient increase. Reduction in substrate areal density and stiffness imparts immediate acceleration and intrinsic responsiveness to impacting droplets (∼350 × g), mitigating the collision and lowering the impalement probability by ∼60% without the need for active actuation. The above results are illustrated with materials ranging from man-made (thin steel or polymer sheets) to nature-made (butterfly wings)1. In the same context, ice accumulation hinders the performance of, and poses safety threats for infrastructure both on the ground and in the air. Previously, rationally designed superhydrophobic surfaces have demonstrated some potential as a passive means to mitigate ice accretion. In this lecture I will discuss ous findings on the collaborative effect of substrate flexibility and surface micro/nanotexture on enhancing both icephobicity and the repellency of viscous droplets (typical of supercooled water). I will demonstrate a passive mechanism for shedding partially solidified (recalescent) droplets–under conditions where partial solidification occurs much faster than the natural droplet oscillation–which does not rely on converting droplet surface energy into kinetic energy (classic recoil mechanism). Using an energy-based model (kinetic-elastic-capillary), we identify a previously unexplored mechanism whereby the substrate oscillation and velocity govern the rebound process, with low-areal density and moderately stiff substrates acting to efficiently absorb the incoming droplet kinetic energy and rectify it back, allowing droplets to overcome adhesion and gravitational forces, and recoil. This mechanism applies for a range of droplet viscosities, spanning from low to high viscosity fluids and even ice slurries, which do not rebound from rigid superhydrophobic substrates.

Four billion people in the world are facing severe water scarcity [1]. To address this problem, mainstream research has been focused on desalination of brine [2], fog/water harvesting from air [3], etc. However, effort to reduce waste water generation from industrial and household activities has not received significant attention. For example, more than 141 million cubic meters of fresh water is used for toilet flushing every day globally [4], which is ~6 times as much as the daily water consumption of the entire Africa population [5]. To greatly reduce the amount of waste water generation in the form of flushing water, toilet surfaces need to remain non-sticky towards both liquids and viscoelastic solid wastes (e.g. urine and human feces). However, achieving both of these functions are very challenging using state-of-the-art superhydrophobic [6] and slippery surfaces [7]. Here, we report the design and fabrication of novel liquid-based coatings that are capable of repelling various liquids and viscoelastic solids, and display excellent anti-biofouling property. We have shown that these coatings can significantly reduce surface adhesion from various viscoelastic solids by ~90% when compared to an untreated smooth surface (e.g. glass). More importantly, the amount of water required to completely clean the surface is only ~10% of those required for typically smooth surfaces. Our results may have important implications for the reduction of waste water generation in industrial and household settings.

Hydrophobic surface treatment using surface roughness and coupling agent was studied for preventing icing performance from frost formation. Poly (vinyl ester) and aluminum plates were used for tests. Diverse fine number of sandpaper was applied on the poly (vinyl ester) for surface roughness whereas aluminate coupling agent was used on the Aluminum. A hydrophobic coating with a static contact angle of 147 was obtained using an aluminate coupling agent on an aluminum (Al) surface, and aluminate coupling agent was first used to create hydrophobic surface. The surface energies of both neat Al and of hydrophobic coating surfaces were determined by both static and dynamic contact angle measurements. After surface treatment, the change of surface energy and degree of hydrophobicity were measured by static contact angle measurement. The shape and thickness of icing per time was measured in low temperature condition. As a result, the decrease in surface energy was observed with hydrophobic surface. The thickness of icing at surface treatment was thinner than neat condition. A hydrophobic surface can effectively reduce adhesion and condensation of water droplets and significantly retard the frosting process at low temperature. Frost formation and deposition on neat Al and hydrophobic coating surfaces were observed using an optical microscope and camera. The experimental results showed that the hydrophobic coating surface obviously restrained frost growth. The variation in frost thickness with time on the surfaces of both neat Al and hydrophobic coating surfaces was measured, and it was found that the frost deposition on hydrophobic coating surface was delayed for 60 min, when compared to a neat Al surface. Fatigue testing was also used to investigate the interfacial durability of the hydrophobic coating on an Al surface. Static contact angle studies in conjunction with fatigue testing revealed that aluminate coupling agent coatings on an Al surface exhibited strong and stable interfacial adhesion. Acknowledgements: this work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MOE) (No. 2016R1D1A1B01012620), 2016-2022, Korea.

Polymer brushes, polymers tethering one end of a surface, are powerful materials for tailoring the surface functionality and morphology towards a wide variety of applications ranging from optical and electronic devices to stem cell researches. In contrast to the 1D and 2D patterns, the fabrication and engineering of well-defined 3D structures of polymer brushes are still in the early stage of development because of the remarkable complexity in simultaneous alignment of the in-plane lateral spacing and the out-of-plane height. This talk will introduce a scanning probe based nanotechnology developed in our laboratory, namely Dip-Pen Nanodisplacement Lithography (DNL), for the fabrication of 3D patterned polymer brushes. The mechanism and attributes of DNL will be firstly discussed. Subsequently, we will focus on how to fabricate 3D patterned polymer brushes by controlling the density of polymer chains or the spacing between nanofeatures made of polymer brushes. Finally, we will introduce some latest development of parallel DNL using multiple cantilevers, and their applications for 1) nanofabrication of metallic 3D structures, and 2) control of cell activities such as cell adhesion and alignment.

We herein report the preparation of durable superhydrophobic and superamphiphobic fabrics by pre-applying precursor materials onto substrates and by subsequently treating the pre-coated substrates with argon-plasma. The coated fabrics showed super-phobicity. The coatings were durable to withstand repeated laundries and multicycles of abrasion without apparently altering the superwettability. The coatings were also very stable in boiling water, strong acid and base, but had little effect on the fabric handle and air permeability. Argon plasma may offer a facile way to prepare durable superwettability fabrics.

Phase change is a classical thermodynamics process involving the phase transitions between liquid-vapor and solid. Over the past century, extensive efforts have been made in the understanding and controlling of phase transition due to its beauty in science and potential applications in the energy saving and national security, power generation, cooling and environment. However, traditional designs are subject to fundamental constraints imposed by the complexity of the multiscale and multiphase process. Learning from nature provides us new insights, new concept, and new methodology to design new surface and new platform to achieve advanced functionalities which are not available using the traditional methods. In this talk, I will discuss our recent efforts in the developing a general bio-inspired approach that can fundamentally change the phase transitions for enhanced phase change heat transfer by controlling surface/interface morphology and chemistry.

Porous hydrophobic and oleophilic materials (PHOMs) have been demonstrated as promising oil sorbent materials for the cleanup of crude-oil spills [1]. In the past decade, with the in-depth understanding of the biomaterials’ surfaces and the development of new materials, various advance oil sorbents have been put forward [2-5]. However, due to their limited absorption capacity, a large quantity of PHOMs would be consumed in oil spill remediation. In this case, the recovery of oil from these sorbents will be a complicated and time-consuming process. Besides, the diffusion of viscous crude oil spill into the inner pores of PHOMs is very slow, which makes it difficult to rapidly clean up crude-oil spills in high viscosity which however is the most common case in marine oil spills.Here, we will present an oil collection device based on the combination of PHOMs and pump, which realized the continuous collection of oil spills in situ from the water surface with high speed and oil/water separation efficiency [6]. Taking advantage of the self-controlled interfaces in the PHOMs, oil/water separation and oil collection could be simultaneously achieved, and the oil sorption capacity is no longer limited to the volume and weight of the sorption material. Furthermore, we will show a joule-heated sorbent design for the fast cleanup of viscous crude-oil spill [ 7]. Since the viscosity of crude oil decreases dramatically with the increase of temperature, the joule heat in situ dicreases the viscosity of crude oil, allowing improved diffusion speed of viscous crude oil through the pores of the oil sorbent. With the aid of joule heating, the oil sorption time could be decreased by 94.6%. To make this joule heating process more energy efficient, we also put forward a confined-heating strategy which dramatically decreased the energy consumption by 65.5%. These contributions will make a big step forward in the design of oil sorbents for future oil spill remediation.

The preparation of multilayer and nanostructured polymer systems involves a layer-by-layer approach where polymer layers can be chemisorbed or physisorbed to formed controlled stacks and thicknesses. This can be done by simple solution chemistry or vapor deposition methods with high layer integrity or undulation of layers. Combinations with grafted polymer brushes and electropolymerization results in new and unprecedented stimuli-response control over several applied fields and magnitudes. In this talk, we will demonstrate superhydrophobic/superhydrophilic and superwetting control based on the use of nanostructured polymer and macromolecular layer-by-layer approaches combined with polymer grafting. By templating, for example, the lotus leaf, it is possible to use hierarchical roughness control followed by reversible wetting behavior with an LCST limited grafted polymer hydrogel. We also report the use of electropolymerization methods to prepare superhydrophobic and oil-water separators based on the doping properties of the conducting polymers. Polybenzoxazine based coatings have also been prepared that show superhydrophobic and superwetting properties with anti-corrosion properties in Carbon steel. Lastly, the use of spray coated hybrid polymer materials enable the preparation of robust superhydrophobic surfaces that are scratch resistant.

In nature, various biological fibrous systems exhibit a unique dynamic wetting property. Here, we revealed the most fundamental of the Chinese brush for its capability in controllable liquid transfer: why must the freshly emergent animal hairs. We demonstrated that the unique anisotropic multi-scale structure of the freshly emergent hairs, featured by the tapered architecture with conical tip enveloped by micro-meter scaled ratcheted squamae, is responsible for the controllable liquid transfer. Inspired by these findings, we developed model devices with double-parallel freshly emergent hairs that allows for direct writing functional microlines with 10 µm resolution and nanometer-thickness, with well-defined profile and uniform distribution on diverse substrates. By brush-coating, a highly oriented DPPDTT and DPPBT polymer thin film were perpared, which deliver over 6 times higher charge carrier mobility compared to the spin-coated films. We envision that the controllable liquid transfer of Chinese brush will shed light on the novel template-free printing of organic composite functional materials devices.

Retarding and preventing frost formation at ultra-low temperature has an increasing importance because of a wide range of applications of ultra-low fluids in aerospace and industrial facilities. Recent efforts for developing anti-frosting surfaces have been mostly devoted to utilizing lotus-leaf-inspired superhydrophobic surfaces. Whether the anti-frosting performance of superhydrophobic surface is still effective under ultra-low temperature has not been elucidated clearly. Here, we investigated the frosting behavior of a fabricated superhydrophobic ZnO nano-arrays under different temperature and different environment. The surface showed excellent performance in anti-condensation and anti-frosting when the surface temperature was ~-20 C degree. Although the frosting event inevitably occurs on all surfaces if decreasing the temperature to -50~-150 C degree,the frost accumulation on the superhydrophobic surfaces always less than the untreated surfaces.Interestingly, the frost layer detaches from the surface within a short time and keep the surface drying in the very beginning of defrosting process. Further, there is no frost formation on the surface at -20 C degree during 10 min testing when blowing compressed air and spraying methanol together or spraying methanol individually. It can reduce the height of the frost layer and increases the density when spraying methanol at -150 C degree. Furthermore, the frost crystals on the upper surface can been blown away due to the low adhesion of ice or frost. It provides a basic idea for solving the frosting problem under ultra-low temperature while combined with other defrosting method.

Addressing water pollution arising from oil spillage and chemical leakage is still challenging and much progress has been made currently toward separating oil-water mixture with high flux by superwetting membranes [1]. However, low mechanical durability is a leading challenge for the real application of super-wetting interfaces due to the weak resistance to physical damage [2]. Moreover, although current ultra-thin membranes with high separation flux are emerging as a potential strategy, the new issue to undergo external mechanical forces or damages was arising [3]. In addition, the robustness against chemical corrosion and biofouling resulted from growth of unwanted marine organisms cannot be ignored as well [4]. Therefore, a new approach for building up a durable superwetting membrane-based oil-water separation system that can withstand a series of harsh conditions, especially for the mechanical damage, was highly desired.Herein, inspired by cobweb structure, we firstly designed the durable carbon nanofiber-polydimethylsiloxane (CNFs-PDMS) network inlay-gated stainless steel mesh (SSM) that shows superhydrophobic and superoleophilicity property for separation. Further, inspired by bufferfly wing scales, single-walled carbon nanotubes were subtly introduced to the improved abrasion-resistant system (ESSM/CNFs-SWCNTs-PDMS) to separate about 100 nm water-in-oil emulsions. These resulting membranes exhibit excellent resistance to harsh environments such as acid, salt, organic, biofouling, and mechanical abrasion treatments. Particularly, mechanical abrasion to the core network for emulsion separation can be avoided using the protective support of metal mesh to ensure super-wetting performance. And also, the SSM/CNFs-PDMS membrane shows a gravity-driven water-in-oil emulsion separation with flux up to 2970 L/m2h1 with high robustness. The ESSM/CNFs-SWCNTs-PDMS can successfully separate around 100 nm emulsions with high durability. Therefore, inspired by cobweb and butterfly wing scales, a brand new route for creating durable and high-flux filtration platforms by combining ultra-thin membranes with the present system also can be significantly developed in the future.References[1] B. Wang et al. Chem. Soc. Rev. 336-361(2015) 44[2] Y. Lu et al. Science 1132-1135 (2015) 347[3] S. Karan et al. Science 1347-1351 (2015) 348[4] S. Pan et al. J. Am. Chem. Soc. 578-581 (2013) 135